The induction of cytokine secretion by rubratoxin B was investigated using human hepatoma cell lines HepG2 and HuH-7. Interleukin (IL)-8, macrophage colony stimulating factor (M-CSF) and granulocyte-macrophage (GM)-CSF were detected in the media of rubratoxin B-treated both cell lines, and their levels peaked at about 40 microg/ml. Rubratoxin B-induced cytokine secretion was enhanced by tumor necrosis factor (TNF)-alpha in HepG2 cells. While emodin increased GM-CSF secretion, the secretion of the others was decreased, indicating that they are regulated differently in rubratoxin B-treated HepG2 cells. To our knowledge, this is the first report that an exogenous stimulus induced the secretion of M-CSF and GM-CSF in hepatocyte-derived hepatoma cells, suggesting that rubratoxin B is an excellent model compound to study the mechanisms of M-CSF and GM-CSF secretion. Our results showed that hepatotoxin rubratoxin B has a potential to induce the secretion of these two CSFs, implying that these factors play roles in rubratoxin B-caused hepatic injury.